Which option would illustrate water hammer due to column rejoining after a void?

Which option would illustrate water hammer due to column rejoining after a void?

• A. Cause of Water Hammer
• B. Rapid valve actuation (valve slam)
• C. Filling of a voided line (column rejoining)
• D. Hot water entering a low pressure line (low pressure discharge)

Answer: (A)

Water hammer from column rejoining occurs when a void forms in the pipe and is suddenly filled as the moving water column reconnects. When the line has a void (air or vapor pocket), the fluid ahead is moving with inertia. If the void is abruptly eliminated, the incoming water rushes to fill it, compressing the trapped vapor and rapidly increasing the pressure. This rapid pressure spike is the hammer associated with column rejoining. Thus, describing the situation as filling of a voided line (column rejoining) best captures this specific mechanism. Other scenarios—such as valve slam from rapid actuation or hot water flashing into a low-pressure line—are different pathways to water hammer, but they involve distinct causes (sudden valve closure/opening or phase-change-driven surges) rather than the rejoining of a separated water column.

Water hammer from column rejoining occurs when a void forms in the pipe and is suddenly filled as the moving water column reconnects. When the line has a void (air or vapor pocket), the fluid ahead is moving with inertia. If the void is abruptly eliminated, the incoming water rushes to fill it, compressing the trapped vapor and rapidly increasing the pressure. This rapid pressure spike is the hammer associated with column rejoining.

Thus, describing the situation as filling of a voided line (column rejoining) best captures this specific mechanism. Other scenarios—such as valve slam from rapid actuation or hot water flashing into a low-pressure line—are different pathways to water hammer, but they involve distinct causes (sudden valve closure/opening or phase-change-driven surges) rather than the rejoining of a separated water column.